### Fall 2000 Physics 102 Hour Exam 2(30 questions)

The grading button and a description of the scoring criteria are at the bottom of this page. Basic questions are marked by a single star *. More difficult questions are marked by two stars **. The most challenging questions are marked by three stars ***.

This exam consists of 30 questions; true-false questions are worth 2 points each, three-choice multiple choice questions are worth 3 points each, five-choice multiple choice questions are worth 6 points each. The maximum possible score is 121. When the exam was given, the mean was 83.9; the median was 84. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1*

A positively-charged particle is moving up as shown. In which magnet position will there be a force on the particle directed out of the page?

(a)
(b)
(c)

### QUESTION 2***

Two identical bar magnets each have a wire loop around them. Loop a is twice as large as loop b. Compare the magnetic flux through the two loops.

(a)   Fa > Fb
(b)   Fa = Fb
(c)   Fa < Fb

### QUESTION 3**

A loop of wire is moved at a constant speed over a fixed permanent magnet as shown above. Which picture below best describes the EMF generated in the loop as a function of position?

(a)
(b)
(c)

### QUESTION 4*

This and the next three questions are about the following situation:

The particle spectrometer shown has a uniform magnetic field in the region of the shaded box with direction perpendicular to the page and magnitude |B| = 0.93 T. Particles #1 through #3, all with the same mass m = 3.34 × 10-27 and same initial velocity v = 2 ´ 106 m/s enter the box at the point shown and follow the trajectories indicted.

Which particle has the greatest magnitude of charge?

(a)   #1
(b)   #2
(c)   #3

### QUESTION 5*

The charge on the particle #3 is determined to be q3 = +1.6 × 10-19 C. What is the distance L labeled on the diagram?

(a)   L = 0.022 m
(b)   L = 0.048 m
(c)   L = 0.090 m

### QUESTION 6*

What is the direction of the magnetic field?

(a)   into the page
(b)   out of the page

### QUESTION 7**

Particles entering the box are given their initial velocity v by acceleration through an electric potential difference V. If the potential difference is increased, the time spent by the particle in the box will

(a)   increase.
(b)   decrease.
(c)   stay the same.

### QUESTION 8*

This and the next two questions are about the following situation:

The self-inductance of a long solenoid is L = µon2V, where n is the number of turns per unit length and V is the volume inside the solenoid. The solenoid below has length l = 0.15 m and cross-sectional area A = 3.5 × 10-4 m2. Its self-inductance is L = 25 mH. A current I of 2.5 amps flows through its coils in the direction shown in the figure.

Which way does the magnetic field point inside the solenoid?

(a)   to the left
(b)   to the right

### QUESTION 9*

How much magnetic energy, Um, is stored in this solenoid?

(a)   Um = 78 mJ
(b)   Um = 123 mJ
(c)   Um = 175 mJ
(d)   Um = 208 mJ
(e)   Um = 345 mJ

### QUESTION 10*

What is the magnetic field inside the solenoid?

(a)   B = 14 mT
(b)   B = 36 mT
(c)   B = 48 mT
(d)   B = 61 mT
(e)   B = 88 mT

### QUESTION 11**

This and the next question are about the following situation:

A single-turn rectangular wire loop of size 20 cm × 30 cm rotates at a uniform rate of w = 50 rad/sec around the z-axis as shown. There is a uniform magnetic field B in the +y direction. The loop has a total resistance of R = 36 W.

At the instant shown, an induced current in the loop will

(a)   flow clockwise.
(b)   flow counterclockwise.
(c)   not flow.

### QUESTION 12**

If the induced rms current in the loop is 0.04 A, what is the strength of the magnetic field B?

(a)   B = 0.17 T
(b)   B = 0.29 T
(c)   B = 0.55 T
(d)   B = 0.68 T
(e)   B = 0.79 T

### QUESTION 13*

This and the next question are about the following situation:

The phasor diagram to the right yields information on a particular series RLC circuit. It is only partially labeled, but you should know from examining it the proper quantity that is referred to by each number, given in ohms, in the drawing.

What is the total impedance, Z, of the circuit?

(a)   Z = 12 W
(b)   Z = 18 W
(c)   Z = 36 W
(d)   Z = 40 W
(e)   Z = 65 W

### QUESTION 14*

If the inductance L = 0.02 H, what is the capacitance?

(a)   C = 0.21 mF
(b)   C = 0.59 mF
(c)   C = 3.17 mF
(d)   C = 17.6 mF
(e)   C = 33.3 mF

### QUESTION 15*

What is the phase angle f for this circuit?

(a)   f = +73.8°
(b)   f = +37.6°
(c)   f = 0
(d)   f = -37.6°
(e)   f = -73.8°

### QUESTION 16**

What is the peak power delivered by the generator?

(a)   Ppk = 3.32 W
(b)   Ppk = 4.13 W
(c)   Ppk = 9.97 W
(d)   Ppk = 14.3 W
(e)   Ppk = 25.9 W

### QUESTION 17*

To bring the circuit closer to resonance, the frequency of the oscillator should be

(a)   increased.
(b)   decreased.

### QUESTION 18***

This and the next question are about the following situation:

Two identical loops are entering a region of uniform magnetic field as shown. They are traveling with equal speed, but loop number 1 is traveling down and loop number 2 is traveling up.

Compare the magnitude of the induced current in the two loops.

(a)   I1 < I2
(b)   I1 = I2
(c)   I1 > I2

### QUESTION 19**

The current in the two loops flow in the same direction (e.g. both clockwise or both counter clockwise).

(T)   True
(F)   False

### QUESTION 20***

This and the next question are about the following situation:

A loop carrying a clockwise current is located to the right of a long straight wire carrying current up as shown.

What is the direction of the magnetic force on the current in the segment a-b of the loop due to the current I1 in the long straight wire?

(a)   up
(b)   down
(c)   into page
(d)   out of page
(e)   zero

### QUESTION 21***

What is the direction of the net force on the loop due to the current in the long straight wire?

(a)   to the left
(b)   to the right
(c)   there is no net force

### QUESTION 22*

This and the next two questions are about the following situation:

An unpolarized electromagnetic wave is incident at a series of three linear polarizers, each with the polarization angle rotated at 45° with respect to the previous one.

The incident wave has an intensity of 1500 W/m2. What is the rms magnitude of the electric field?

(a)   E = 212 N/C
(b)   E = 347 N/C
(c)   E = 554 N/C
(d)   E = 631 N/C
(e)   E = 752 N/C

### QUESTION 23*

After the first polarizer, the light is linearly-polarized. When it passes through the second polarizer

(a)   only the electric field is reduced.
(b)   only the magnetic field is reduced.
(c)   both the electric and magnetic field are reduced.

### QUESTION 24**

If the initial intensity of the unpolarized light is I0, what is the intensity I3 transmitted by the stack?

(a)   I3 = 0
(b)   I3 = 0.50 I0
(c)   I3 = 0.25 I0
(d)   I3 = 0.125 I0
(e)   I3 = 0.0625 I0

### QUESTION 25**

Jeep A traveling east at 50 mph looks behind and observes the lights of a police car following him with speed 70 mph. Chasing the police car is Jeep B traveling at 90 mph.

Compare the frequency of the light from the police car that Jeep A observes (fA) with that observed by Jeep B (fB).

(a)   fA > fB
(b)   fA = fB
(c)   fA < fB

### QUESTION 26**

This and the next question are about the following situation:

Three long co-planar parallel wires carrying currents are oriented as shown.

The magnitude of the force on a 1 meter long section of the middle wire (#2) from the currents flowing in the other two is:

(a)   F = 1.08 × 10-4 N
(b)   F = 3.34 × 10-4 N
(c)   F = 6.61 × 10-4 N
(d)   F = 7.90 × 10-4 N
(e)   F = 8.41 × 10-4 N

### QUESTION 27*

The direction of the force on wire #2 is:

(a)   up
(b)   down

### QUESTION 28**

The figure below shows an edge view of two identical current-carrying loops oriented as shown in a uniform magnetic field.

Compare the magnitude of the torque t 1 on loop #1 with the torque t 2 on loop #2 at the instant shown.

(a)   t1 > t2
(b)   t1 = t2
(c)   t1 < t2

### QUESTION 29**

This and the next question are about the following situation:

A square coil with sides of 5 cm is wound with 20 turns of wire that has resistance per length of 3 W/m. A coil is placed in a uniform magnetic field oriented perpendicular to the plane of the loop that is increased linearly from 0 to 4 T in 60 seconds.

Find the induced current in the loop while the field is increasing.

(a)   I = 0.278 mA
(b)   I = 0.442 mA
(c)   I = 0.792 mA
(d)   I = 1.020 mA
(e)   I = 1.421 mA

### QUESTION 30***

If the number of turns in the coil is increased, the induced current:

(a)   increases
(b)   stays the same
(c)   decreases

Scoring of True-False (T,F) Questions:
• If you mark the correct answer, you get 2 points.
• If you mark the wrong answer or if you mark neither answer, you get 0 points.
Scoring of Multiple Choice I (a,b,c) Questions:
• If you mark the correct answer, you get 3 points.
• If you mark a wrong answer or if you mark none of the answers, you get 0 points.
Scoring of Multiple Choice II (a,b,c,d,e) Questions:
• If you mark one answer and it is the correct answer, you get 6 points.
• If you mark two answers and one of them is the correct answer, you get 3 points.
• If you mark three answers and one of them is the correct answer, you get 2 points.
• If you do not mark the correct answer, or if you mark more than three answers, or if you mark none of the answers, you get 0 points.